(CNN) -- American cyclist Lance Armstrong suffered a shattering blow in his comeback bid on Monday when he broke his right collarbone after falling on the first stage of a five-day race in northern Spain.
American Armstrong was competing in Spain to regain full race fitness after coming out of retirement.

Emerging from a hospital with his arm in a sling, Armstrong said he will return to the United States, where doctors will determined whether he needs surgery.

"I'm miserable," said the record seven-time Tour de France champion. "I just need to relax a couple of days and then make a plan."

Armstrong could be out for three to four weeks said Jacinto Vidarte, spokesman for the Vuelta Ciclista Castilla y Leon race, following a crash that involved a group of 15 to 20 riders some 20 kilometers from the finish.

The injury looks certain to end Armstrong's hopes of challenging for the Giro d'Italia from May 9-31 and must cast big doubts on his plans to chase an eighth Tour crown from July 4-26 in France.

The 37-year-old Armstrong was taken to a hospital by ambulance and was seen pointing to his collarbone, CNN's Al Goodman reported from northern Spain.

Armstrong, who came out of retirement after more than three years to return to competitive cycling with Astana in January, walked to the ambulance unaided, television pictures from the scene showed.

Bartosz Huzarski, a cyclist racing for the Italian team ISD, saw the fall, but said he did not know what had caused it. Only Armstrong appeared to indicate he was hurt, the Polish cyclist said.

The fall took place a on a sunny day on a stretch of two-lane highway, Goodman said, as riders tackled the 104-mile (168-km) opening stage, as Armstrong stepped up his latest return to the sport.